A local oscillator, LO, for use as a signal source is an important building block in many communications systems and radar systems. In an LO, a low phase noise is often needed in order to achieve a high performance of the overall system in which the LO is comprised.
Examples of oscillator technologies that are often used in LOs are Radio Frequency Integrated Circuits (RFIC) oscillators, and Monolithic Microwave integrated Circuits (MMIC) oscillators. For both RFIC and MMIC oscillators, their phase noise performance is limited mainly by the quality factor Q of an on-chip resonator which is comprised in the oscillator. The resonator will often comprise a varactor or a fixed capacitor, as well as an inductor.
Attempts have been made to address the issue of phase noise in LOs. These attempts have mainly concentrated on improving the Q-factor of the resonator's inductor. However, at higher frequencies, for example at frequencies above 20 GHz, these attempts have not been as successful as would have been desired.
Document EP 1 926 207 A1 discloses an oscillator circuit which comprises a fine tuning network, a coarse tuning network and a dynamically tuned dual coupled resonator network.